This invention relates to a roller frictional transmission unit used as a transfer of a four wheel drive vehicle, and more specifically to an art to improve a durability of a thrust bearing arranged to position a roller of the transmission unit in an axial direction.
U.S. Patent Application Publication No. 2010/0276246 A1 (corresponding to Japanese Patent Application Publication No. 2009-173261) discloses a roller frictional transmission unit including a pair of rollers. In this roller frictional transmission unit, outer circumference surfaces of the rollers are pressed and contacted with each other in a radial direction so as to transmit power between the rollers by the friction. One of the rollers is connected with an input shaft connected with a driving system of main driving wheels of a four wheel drive vehicle. Other of the rollers is connected with a driving system of auxiliary driving wheels of the four wheel driving vehicle.
In the roller frictional transmission unit, each of the rollers is positioned by thrust bearings disposed on both sides in an axial direction, with respect to a housing of the roller frictional transmission unit in the axial direction, so as to stably perform the frictional contact between the rollers.